The determination of clinically relevant parameters in plasma and serum samples can be significantly influenced by elevated triglyceride concentrations (lipemia). Lipemic samples with elevated triglyceride concentration occur relatively frequently and can, for example, be caused by a high-fat diet, diabetes mellitus, chronic kidney failure, pancreatitis, lupus erythematosus, multiple myeloma, or the intake of medicaments or oral contraceptives.
The interfering effect of elevated triglyceride concentrations is primarily based on the clouding (turbidity) of the samples, which is sometimes visible to the naked eye and which results in an increased light scattering and absorption. This phenomenon interferes with photometric assay systems most of all. A further interfering effect is that the solubility of an analyte to be detected can be impaired.
Therefore, modern automatic analyzers increasingly comprise so-called preanalytical analysis units, in which the sample material is analyzed with respect to any interference substances, such as lipids, hemoglobin and bilirubin, before the actual determination of one or more specific analytes is carried out. If critical amounts of one or more interference substances are established in a sample, it is, for example, possible to provide the assay results obtained for the sample with a warning, meaning that a user is informed that a false result has possibly been measured here.
Since the triglyceride concentration which causes a significant interference is different for each assay and depends on the analyzer used, the regents used, etc., it is necessary to carry out interference studies for each assay in order to ascertain from which triglyceride concentration a specific assay no longer provides reliable assay results.
A problem is that there is as yet no standardized lipemic sample material, which is required for carrying out the interference studies. To date, Intralipid, a soybean lipid emulsion, is frequently added to human plasma samples or plasma pools in order to simulate lipemic interferences. However, it has been found that the addition of Intralipid is not a generally applicable method of lipid-interference determination, because the interferences caused by Intralipid do not correlate in all cases with the interferences occurring in native lipemic samples (Bornhorst, J. A. et al., Assay-specific differences in lipemic interference in native and Intralipid-supplemented samples. Clin. Chem. 2004, 50(11): 2197-2201). Therefore, it is preferred to use lipemic donor samples for interference studies.
However, sufficient amounts of native lipemic patient samples, particularly those with exceptionally high triglyceride concentrations (>500 mg/dL), are only obtainable with a very high degree of effort, since extremely large donor groups would have to be examined.